This application is based on and claims priority under U.S.C. xc2xa7119 with respect to Japanese Application No. 2001-053004 filed on Feb. 27, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
This invention generally relates to vehicle braking. More particularly, the present invention pertains to a brake master cylinder for a hydraulic pressure type braking device of a vehicle.
2. Background of the Invention
A variety of plunger type brake master cylinders are known in the art. These plunger type brake master cylinders possess the advantage of shortening the axial length of the brake master cylinder. Known plunger type brake master cylinders include a plurality of sealing members engaged with a cylinder body and provided between the internal periphery of the cylinder body and the outer periphery of pistons for defining first and second pressure chambers. The external diameter of first and second pistons of the known plunger type brake master cylinder is constant through substantially the entire length of the pistons. Examples of known brake master cylinders having such a construction are disclosed in Japanese Patent Laid-Open Publication No. H06-298072, Japanese Patent Laid-Open Publication No. H11-512681, U.S. Pat. No. 4,524,585, and U.S. Pat. No.6,012,288.
According to the known brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H06-298072 and Japanese Patent Laid-Open Publication No. H11-512681, an annular member is provided between the inner peripheral surface of the cylinder body and the outer peripheral surface of the second piston, and the annular member is fixed on the cylinder body. In addition, sealing members for defining the first pressure chamber are provided on the internal diameter side and the external diameter side of the annular member respectively. Thus, the internal diameter of the cylinder body cannot be made to be approximately the same size as the external diameter of the piston. This brings about the drawback that the external diameter of the cylinder body becomes relatively large. Particularly with respect to the brake master cylinder disclosed in Japanese Patent Laid-Open Publication No. H06-298072, because a cap is positioned on the inner periphery of the cylinder body and a sleeve is positioned on the inner peripheral side of the cap, the total weight of the master cylinder becomes relatively large in accordance with the relatively large external diameter of the cylinder body.
In the brake master cylinder disclosed in U.S. Pat. No. 4,524,585, although the external diameter of the cylinder body can be relatively small because the sealing member for defining the pressure chamber is provided in an annular groove formed on the inner periphery of the cylinder body, the air is confined in the annular groove by the sealing member. Thus, this brake master cylinder suffers from the drawback that air bleeding is not performed. This brake master cylinder also suffers from the drawback that the assembling performance of the sealing member is significantly retarded.
With the brake master cylinder disclosed in U.S. Pat. No. 6,012,288, the cylinder body includes openings on both ends of cylinder bores and both ends of the cylinder bores are closed with plug-shaped members respectively. With this construction, the brake master cylinder is not sufficiently reliable.
A need thus exists for a brake master cylinder which is not as susceptible to the disadvantages and drawbacks discussed above.
According to one aspect, a brake master cylinder includes a cylinder body having a cylinder bore including a closed end and an open end, a plug shaped member positioned in the open end of the cylinder bore and secured to the cylinder body, a first piston slidably extending through the plug shaped member, a second piston positioned in the cylinder bore, a first sealing member engaged with the outer periphery of the first piston and the inner periphery of the cylinder body to be supported by the cylinder body, a second sealing member engaged with the outer periphery of the second piston and the inner periphery of the cylinder body to be supported by the cylinder body, and a third sealing member positioned between the second sealing member and the closed end of the cylinder bore and engaged with the outer peripheral surface of the second piston and the inner peripheral surface of the cylinder body to be supported by the cylinder body. A first pressure chamber has one end defined by the second piston and the second sealing member and the other end defined by the first piston and the first sealing member, while a second pressure chamber has one end defined by the cylinder body and the other end defined by the second piston and the third sealing member. A piston return mechanism is adapted to return the first piston and the second piston to respective return positions. A first radial bore is formed on the first piston and is movable from one side of the sealing member to the other side upon sliding movement of the first piston from the return position toward the closed end of the cylinder bore, and establishes communication between the first pressure chamber and a reservoir when the first piston is positioned at the return position. A second radial bore is formed on the second piston and is movable from one side of the third sealing member toward the other side of the third sealing member upon sliding movement of the second piston from the return position toward the closed end of the cylinder bore, and establishes communication between the second pressure chamber and the reservoir when the second piston is positioned at the return position. An annular member supported at the cylinder body is positioned between the second sealing member and the third sealing member for supporting the second and third sealing members by the cylinder body.
According to another aspect, a brake master cylinder includes a cylinder body having a cylinder bore closed at one end and open at an opposite end, a plug member threadably engaged with the cylinder body at the open end of the cylinder bore, an axially movable first piston passing through the plug member and provided with a first through bore in a wall of the first piston, an axially movable second piston positioned in the cylinder bore and provided with a second through bore in a wall of the second piston, a first sealing member providing a liquid-tight seal between the outer periphery of the first piston and the inner periphery of the cylinder body, a second sealing member providing a liquid-tight seal between an outer periphery of the second piston and the inner periphery of the cylinder body, and a third sealing member located axially between the second sealing member and the closed end of the cylinder bore and providing a liquid-tight seal between the outer peripheral surface of the second piston and the inner peripheral surface of the cylinder body. A first pressure chamber is defined in the cylinder bore between the first piston and the second piston, and a second pressure chamber is defined in the cylinder bore between the closed end of the cylinder bore and the second piston. Respective springs each apply a force to one of the first and second pistons to urge the first piston and the second piston to respective return positions at which the first through bore provides communication between the first pressure chamber and a first reservoir inlet formed in the cylinder bore and the second through bore provides communication between the second pressure chamber and a second reservoir inlet formed in the cylinder bore. The first through bore of the first piston is movable relative to the first sealing member upon sliding movement of the first piston from the return position toward the closed end of the cylinder bore, and the second through bore of the second piston is movable relative to the third sealing member upon sliding movement of the second piston from the return position toward the closed end of the cylinder bore. An annular member is supported at the cylinder bore by a support member, and is positioned between the second sealing member and the third sealing member to support the second and third sealing members.